Ghrelin neutralization during fasting-refeeding cycle impairs the recuperation of body weight and alters hepatic energy metabolism

Regulation of peripheral tissue substrate metabolism by the gut-derived hormone ghrelin

Ghrelin increases in the circulation prior to entrained mealtimes, with the acylated (AG) form functioning to stimulate food intake and growth hormone release. Acutely, AG induces whole-body insulin resistance, potentially to maintain glycemia between meals. Alternatively, chronic administration of both AG and the unacylated isoform of ghrelin (unAG) is associated with improved skeletal muscle insulin sensitivity as well as reduced intramuscular lipids and inflammation. This may be due to effects on lipid metabolism, with ghrelin promoting storage of fat in adipose and liver while stimulating oxidation in skeletal muscle, preventing ectopic lipid accumulation. This is of specific relevance in the handling of meal-derived lipids, as ghrelin rises preprandially with effects persisting for 2-3 h following exposure in skeletal muscle, coinciding with elevated plasma FFAs. We hypothesize that ghrelin acts as a preparatory signal for incoming lipids, as well as a regulatory hormone for their use and storage. The effects of ghrelin on skeletal muscle are lost with high fat diet feeding and physical inactivity, potentially being implicated in the pathogenesis of metabolic disease. This review summarizes the metabolic effects of both ghrelin isoforms on peripheral tissues including the pancreas, adipose, liver, and skeletal muscle. Additionally, we speculate on the physiological relevance of these effects in vivo and suggest that ghrelin may be a key regulatory hormone for nutrient handling in the postprandial state.

Turning the clock forward: New pharmacological and non pharmacological targets for the treatment of obesity

AIMS

Obesity and its main metabolic complication, type 2 diabetes, have attained the status of a global pandemic; there is need for novel strategies aimed at treating obesity and preventing the development of diabetes. A healthy diet and exercise are basic for treatment of obesity but often not enough. Pharmacotherapy can be helpful in maintaining compliance, ameliorating obesity-related health risks, and improving quality of life. In the last two decades, the knowledge of central and peripheral mechanisms underlying homeostatic and hedonic aspects of food intake has significantly increased. Dysregulation of one or more of these components could lead to obesity.

DATA SYNTHESIS

In order to better understand how potential innovative treatment options can affect obesity, homeostatic and reward mechanisms that regulate energy balance has been firstly illustrated. Then, an overview of potential therapeutic targets for obesity, distinguished according to the level of regulation of feeding behavior, has been provided. Moreover, several non-drug therapies have been recently tested in obesity, such as non-invasive neurostimulation: Transcranial Magnetic Stimulation or Transcranial Direct Current Stimulation. All of them are promising for obesity treatment and are almost devoid of side effects, constituting a potential resource for the prevention of metabolic diseases.

CONCLUSIONS

The plethora of current anti-obesity therapies creates the unique challenge for physicians to customize the intervention, according to the specific obesity characteristics and the intervention side effect profiles; moreover, it allows multimodal approaches addressed to treat obesity and metabolic adaptation with complementary mechanisms.

Response of metabolic hormones and blood metabolites to realimentation in rehabilitated harbor seal (Phoca vitulina) pups

Mammals with increased requirements for adipose tissue stores, such as marine mammals, have altered nutrient allocation priorities compared to many terrestrial mammals and thus the physiological response to undernutrition (low nutritional status) and realimentation (refeeding) may differ. Key regulators of nutrient allocation and tissue specific growth include metabolic hormones of the somatotropic axis, growth hormone (GH) and insulin-like growth factor (IGF)-I, as well as satiety and adipose promoting ghrelin and the stress hormone cortisol. Longitudinal measurements of metabolic hormones, blood metabolites, and morphometrics were collected over a 10-week period in twelve (male n = 3, female n = 9) harbor seal pups (< 6 weeks of age). Blood metabolites were used to indicate metabolic response during realimentation while morphometrics estimated tissue specific growth priorities. Harbor seal pups undergoing refeeding after nutritional deprivation show a preference for protein sparing despite severe malnutrition. Both BUN and total protein were negatively associated with GH and positively associated with IGF-I and ghrelin highlighting the importance of these metabolic hormones in the regulation of protein metabolism. While the response of the somatotropic axis to realimentation was typical of the mammalian pattern, the surprising increase of ghrelin across the study period suggests the priority of adipose accretion in addition to a possible mechanism regulating compensatory growth of vital adipose stores in a species, which prioritizes adipose accretion for survival.

Beneficial Effects of Bariatric Surgery-Induced by Weight Loss on the Proteome of Abdominal Subcutaneous Adipose Tissue

Bariatric surgery (BS) is the most effective treatment for obesity and has a positive impact on cardiometabolic risk and in the remission of type 2 diabetes. Following BS, the majority of fat mass is lost from the subcutaneous adipose tissue depot (SAT). However, the changes in this depot and functions and as well as its relative contribution to the beneficial effects of this surgery are still controversial. With the aim of studying altered proteins and molecular pathways in abdominal SAT (aSAT) after body weight normalization induced by BS, we carried out a proteomic approach sequential window acquisition of all theoretical mass spectra (SWATH-MS) analysis. These results were complemented by Western blot, electron microscopy and RT-qPCR. With all of the working tools mentioned, we confirmed that after BS, up-regulated proteins were associated with metabolism, the citric acid cycle and respiratory electron transport, triglyceride catabolism and metabolism, formation of ATP, pyruvate metabolism, glycolysis/gluconeogenesis and thermogenesis among others. In contrast, proteins with decreased values are part of the biological pathways related to the immune system. We also confirmed that obesity caused a significant decrease in mitochondrial density and coverage, which was corrected by BS. Together, these findings reveal specific molecular mechanisms, genes and proteins that improve adipose tissue function after BS characterized by lower inflammation, increased glucose uptake, higher insulin sensitivity, higher de novo lipogenesis, increased mitochondrial function and decreased adipocyte size.

Pharmacological Modulation of Ghrelin to Induce Weight Loss: Successes and Challenges

PURPOSE OF REVIEW

Obesity is affecting over 600 million adults worldwide and has numerous negative effects on health. Since ghrelin positively regulates food intake and body weight, targeting its signaling to induce weight loss under conditions of obesity seems promising. Thus, the present work reviews and discusses different possibilities to alter ghrelin signaling.

RECENT FINDINGS

Ghrelin signaling can be altered by RNA Spiegelmers, GHSR/Fc, ghrelin-O-acyltransferase inhibitors as well as antagonists, and inverse agonists of the ghrelin receptor. PF-05190457 is the first inverse agonist of the ghrelin receptor tested in humans shown to inhibit growth hormone secretion, gastric emptying, and reduce postprandial glucose levels. Effects on body weight were not examined. Although various highly promising agents targeting ghrelin signaling exist, so far, they were mostly only tested in vitro or in animal models. Further research in humans is thus needed to further assess the effects of ghrelin antagonism on body weight especially under conditions of obesity.

Endocrine response to realimentation in young northern elephant seals (Mirounga angustirostris): Indications for development of fasting adaptation

Most organisms undergo changes in their environment, both predictably and unpredictably, which require them to alter priorities in nutrient allocation with regards to food availability. Species that more predictably encounter extended periods of limited food resources or intake while mitigating the negative effects of starvation are considered to be fasting adapted. Northern elephant seals (NES) are one such species and routinely undergo extended periods of fasting for breeding, molting, as well as a post-weaning fast at 6-8weeks of age. However, during unusual times of nutritional deprivation, animals may enter stage III fasting. While fasting and foraging in this species has been extensively studied, realimentation following fasting beyond normal life history parameters has not been investigated. In this study, changes in ghrelin, growth hormone (GH), and insulin-like growth factor (IGF)-I were compared across 8weeks of realimentation following emaciation in three age classes: neonates, post-molt pups, and yearlings. Longitudinal changes in hormone profiles indicate that neonate and post-molt pups are slow to recover mass and positive energy balance despite an energy dense diet fed at 10% body mass. In addition, ghrelin and GH concentrations remained elevated in post-molt pups compared to other age classes. Changes in hormone concentrations early in realimentation indicate that yearling animals recover more rapidly from periods of nutritional deprivation than do younger animals. Overall, this suggests that the ability to regulate metabolic homeostasis with regards to nutrient allocation may develop over time, even in a species that is considered to be fasting adapted.

Turning mirror-image oligonucleotides into drugs: the evolution of Spiegelmer(®) therapeutics

Spiegelmers are synthetic target-binding oligonucleotides built from non-natural l-nucleotides. Like aptamers, Spiegelmers fold into distinct shapes that bind the targets with high affinity and selectivity. Furthermore, the mirror-image configuration confers plasma stability and immunological passivity. Various Spiegelmers against pharmacologically attractive targets were shown to be efficacious in animal models. Three Spiegelmer candidates: emapticap pegol (NOX-E36; anti-CCL2), olaptesed pegol (NOX-A12; anti-CXCL12) and lexaptepid pegol (NOX-H94; anti-hepcidin), underwent regulatory safety studies, demonstrated good safety profiles in healthy volunteers and were taken into Phase IIa studies in patients. Proof-of-concept for emapticap pegol has recently been demonstrated in diabetic nephropathy patients. Furthermore, promising interim Phase IIa data of olaptesed pegol and lexapteptid pegol also suggest efficacy in the respective patient populations.

Anti-ghrelin Spiegelmer inhibits exogenous ghrelin-induced increases in food intake, hoarding, and neural activation, but not food deprivation-induced increases

Circulating concentrations of the stomach-derived "hunger-peptide" ghrelin increase in direct proportion to the time since the last meal. Exogenous ghrelin also increases food intake in rodents and humans, suggesting ghrelin may increase post-fast ingestive behaviors. Food intake after food deprivation is increased by laboratory rats and mice, but not by humans (despite dogma to the contrary) or by Siberian hamsters; instead, humans and Siberian hamsters increase food hoarding, suggesting the latter as a model of fasting-induced changes in human ingestive behavior. Exogenous ghrelin markedly increases food hoarding by ad libitum-fed Siberian hamsters similarly to that after food deprivation, indicating sufficiency. Here, we tested the necessity of ghrelin to increase food foraging, food hoarding, and food intake, and neural activation [c-Fos immunoreactivity (c-Fos-ir)] using anti-ghrelin Spiegelmer NOX-B11-2 (SPM), an l-oligonucleotide that specifically binds active ghrelin, inhibiting peptide-receptor interaction. SPM blocked exogenous ghrelin-induced increases in food hoarding the first 2 days after injection, and foraging and food intake at 1-2 h and 2-4 h, respectively, and inhibited hypothalamic c-Fos-ir. SPM given every 24 h across 48-h food deprivation inconsistently inhibited food hoarding after refeeding and c-Fos-ir, similarly to inabilities to do so in laboratory rats and mice. These results suggest that ghrelin may not be necessary for food deprivation-induced foraging and hoarding and neural activation. A possible compensatory response, however, may underlie these findings because SPM treatment led to marked increases in circulating ghrelin concentrations. Collectively, these results show that SPM can block exogenous ghrelin-induced ingestive behaviors, but the necessity of ghrelin for food deprivation-induced ingestive behaviors remains unclear.

Place of preoperative treatment of acromegaly with somatostatin analog on surgical outcome: a systematic review and meta-analysis

Context

Transsphenoidal neurosurgery is the accepted first-line treatment of acromegaly in the majority of patients. Previous studies addressing preoperative somatostatin analog (SSA) treatment and subsequent surgical cure rates are conflicting, reporting either benefits or no significant differences.

Objective

The aim of this study, based on a meta-analysis of all published reports, was to investigate whether treatment with SSA before surgery improves the surgical outcome of acromegaly.

Data Sources

All studies of preoperative treatment of acromegaly with SSA were systematically reviewed up to December 2011. We searched the Medline, Embase, Cochrane and Google Scholar electronic databases. Study Selection: The primary endpoint was the biochemical postoperative cure rate. We identified 286 studies, out of which 10 studies (3.49%) fulfilling the eligibility criteria were selected for analysis; five retrospective studies with a control group, two prospective non-randomized trials, and three prospective controlled trials. The meta-analysis was conducted using the random-effects model.

Data Extraction

Data were extracted from published reports by two independent observers. Data Synthesis: A borderline effect was detected in the analysis of all of the trials with control groups, with a pooled odds ratio (OR) for biochemical cure with SSA treatment of 1.62 (95% CI, 0.93–2.82). In the analysis of the three prospective controlled trials, a statistically significant effect was idenfified OR: 3.62 (95% CI, 1.88–6.96).

Conclusions

Preoperative treatment with SSA og GH-secreting pituitary adenomas shows a significant improvement on surgical results. This meta-analysis suggests that in centers without optimal results all patients with a GH-secreting pituitary macroadenoma should be treated with a long-acting SSA prior to surgical treatment.

Clinical manifestations and diagnosis of acromegaly

Acromegaly and gigantism are due to excess GH production, usually as a result of a pituitary adenoma. The incidence of acromegaly is 5 cases per million per year and the prevalence is 60 cases per million. Clinical manifestations in each patient depend on the levels of GH and IGF-I, age, tumor size, and the delay in diagnosis. Manifestations of acromegaly are varied and include acral and soft tissue overgrowth, joint pain, diabetes mellitus, hypertension, and heart and respiratory failure. Acromegaly is a disabling disease that is associated with increased morbidity and reduced life expectancy. The diagnosis is based primarily on clinical features and confirmed by measuring GH levels after oral glucose loading and the estimation of IGF-I. It has been suggested that the rate of mortality in patients with acromegaly is correlated with the degree of control of GH. Adequately treated, the relative mortality risk can be markedly reduced towards normal.

[Endocrine function in obesity]

Obesity is associated to significant disturbances in endocrine function. Hyper insulinemia and insulin resistance are the best known changes in obesity, but their mechanisms and clinical significance are not clearly established. Adipose tissue is considered to be a hormone-secreting endocrine organ; and increased leptin secretion from the adipocyte, a satiety signal, is a well-established endocrine change in obesity. In obesity there is a decreased GH secretion. Impairment of somatotropic function in obesity is functional and may be reversed in certain circumstances. The pathophysiological mechanism responsible for low GH secretion in obesity is probably multifactorial. There are many data suggesting that a chronic state of somatostatin hypersecretion results in inhibition of GH release. Increased FFA levels, as well as a deficient ghrelin secretion, probably contribute to the impaired GH secretion. In women, abdominal obesity is associated to hyperandrogenism and low sex hormone-binding globulin levels. Obese men, particularly those with morbid obesity, have decreased testosterone and gonadotropin levels. Obesity is associated to an increased cortisol production rate, which is compensated for by a higher cortisol clearance, resulting in plasma free cortisol levels that do not change when body weight increases. Ghrelin is the only known circulating orexigenic factor, and has been found to be decreased in obese people. In obesity there is also a trend to increased TSH and free T3 levels.